Sorry for the late response but....
Answer:
36 cents
Explanation:
First, we would want to calculate how much the box would sell for before the sister ate some.
We would get 38*29(in cents) and we can further get 1102 cents before the sister ate the candy bars.
The sister ate 7 candy bars leaving us with 31 candy bars. In order to deduct the price for each candy bar, it would be a situation like the following:
$6 for 3 boxes of 500 cookies (i know that's cheap)
6/3...
$2 per box.
Using our situation we get 1102 cents for 31 candy bars.
1102 cents/31...
35.5483871
That does seem unrealistic, so we round to the nearest whole number and we get...
36 cents